Amorphous hydrogenated carbon (a-C:H) films have been deposited using a variety of chemical vapor deposition (CVD) techniques wherein a chemical process taking place in the vapor phase of the gas next to the substrate causes the reaction product to be deposited. One prior art technique involves placing a substrate for deposition in a reaction chamber and heating the substrate to a temperature of 800.degree. C. to 1000.degree. C. Hydrogen gas is then fed into the reaction chamber, and microwave power is applied at 1 kilowatt with a frequency of 2.45 GHz. A magnetic field of about 2000 Gauss is simultaneously applied to the reaction chamber for forming an electron cyclotron resonance condition in the reaction chamber so that the plasma electrons will be caused to orbit the magnetic field at a resonant frequency and trap or confine the plasma ions.
A carbon compound gas, that acts as a catalyst, is introduced into the reaction chamber at a relatively high pressure of up to 760 Torr. The catalytic gas, in combination with the magnetic field and microwave power, allows a hard carbon film to be formed on a substrate disposed in the reaction chamber.
A disadvantage of this method is that catalytic gases containing minerals such as nickel, manganese, or germanium must be introduced into the system to be used as a catalyst. Another disadvantage is that heat sensitive substrates, such as plastic, are unable to withstand these high temperatures. The discussed method is disclosed in U.S. Pat. No. 4,871,581, by S. Yamazaki.
A similar prior art method of depositing diamond-like films on a substrate is disclosed in U.S. Pat. No. 4,935,303, by Ikoma et al. In the disclosed method, a first magnetic field of 1300 Gauss is applied to a plasma producing chamber, and a second magnetic field of 875 Gauss is applied near the surface of a substrate. The substrate is maintained at a temperature between 350.degree. C. and 700.degree. C., with 580.degree. C. being preferred. If the substrate is not maintained above 350.degree. C., a diamond-like film may not form on the substrate. If a film is formed, the hydrogen content was excessively high and the film is too low in density, resulting in low chemical and structural stability.
Again, a disadvantage to the above method, is the inability to form diamond-like films on substrates at temperatures less than 350.degree. C. Another disadvantage of the method is its requirement of a substantially strong magnetic field.
Accordingly, a method of depositing films, with such properties as extreme hardness, optical transparency, and chemical inertness, onto substrates that are heat sensitive, would be a solution to these problems.